The invention relates to a method for setting up connections or calls in a communication system including at least one first communication network having a number of first terminals connected thereto and at least one second communication network having a number of second terminals connected thereto. The connections or calls between a respective first terminal and a respective second terminal are being routed through one or more access servers which may be part of the first or second communication network. The invention can be used in all kinds of packet switched networks (not only in IP-based networks; IP: internet protocol).
In particular the invention relates to terminating calls or connections from a packet switch network to a terminal of a circuit switched network through one or more access servers. For example, the invention relates to a situation where speech (e.g. voice over IP) and data calls terminating from a TCP/IP based network (e.g. Internet) are routed to a subscriber (or respectively to his/her terminal equipment) in a telecommunication network. The telecommunication network may be a public land mobile network PLMN, a public switched telephone network PSTN or an integrated services digital network ISDN. All such telecommunication networks are intrinsically based on circuit switching rather than a packet switching.
1. Background of the Invention
An access server is a well-known functionality in TCP/IP and/or telecommunication networks. FIG. 4a shows a number of terminals TE1-TE4 connected to an internet/intranet. In this case an access server AS provides the functionality to enable direct internet/intranet access. As shown in FIG. 4b, the access server AS may also provide an interface between the packet switched network (e.g. a TCP/IP network) and a circuit switched network (such as a public switched telephone network PSTN). It should be noted in FIG. 4b that geographically the entities of the packet switched network and the circuit switched network will overlap. Therefore, the access server AS provides the functional interconnection between entities in the two networks rather than the geographical interface. It is also not important to which network (packet switched or circuit switched network) the access server AS is attributed as long as it provides the functional interconnection between the first and second network, in the case of an interconnection between a packet switched network and a circuit switched network in particular the mapping of a packet switched call from a terminal TE of the first network to a circuit switched call to be terminated in the terminal MS of the second network.
In case the second network is constituted by a mobile radio communication network (such as the D1, D2 or E-plus network in Germany), there may be provided several access servers AS and furthermore the mobile stations MS constituting the second terminals of the second network are mobile, i.e. they roam from cell to cell in the mobile radio communication network.
TELNET Session According to the Prior Art
When a plurality of access servers AS including one gateway access server GAS are provided, one access server AS is used as the final device for the packet switching of the call and the access server AS then converts the packet switched (call) connection to a circuit switched connection (call) between the access server AS and the terminal of the circuit switched network. This may for example be the case, when a mobile station MS is not connected with an IP address (otherwise packet switching may be used end-to-end). FIG. 4c shows steps {circle around (1)}-{circle around (3)} to set up a (call) connection from a terminal TE of a TCP/IP network to a terminal MS of a telecommunication network. In FIG. 4c only for illustration purposes the access servers AS1, AS2 are located in the telecommunication network.
The TELNET session is just an example of how such a (call) connection setup can be done. It is also possible to provide a special translation (address translation) even for a telecommunication network that converts from IP address to MSISDN number, e.g. in cases where subscribers have fixed IP addresses.
In step {circle around (1)} a call from a terminal of the TCP/IP network can be terminated into the telecommunication network. When sending a call set up message (actually this is the first packet transmitted), the terminal TE also includes an identification of the called mobile station MS to which a call is to be set up. The TELNET session is used to retrieve the IP address (either a fixed IP address or a dynamically allocated IP address when the mobile subscriber accesses the TCP/IP network) by sending as identification for the called mobile station the mobile station subscriber number MSISDN in step {circle around (2)} to the access server AS1 or AS2 depending on which access server is provided for serving the mobile station MS. (Moreover, instead of the MSISDN also the IMSI may be used (in mobile radio networks); even more generally E.164 numbers are used such that the concept is generally applicable to PSTN and ISDN as well). In step {circle around (3)} the access server, e.g. AS1, returns the IP address of the mobile station MS. Of course, it will be appreciated that the mobile station MS roams in said telecommunication network such that depending on the location it will be served by a mobile switching center MSC1 or a mobile switching center MSC2 as illustrated in FIG. 4c. 
Whilst the TELNET session can in principle return the IP address of the mobile station, there are some intrinsic problems with the TELNET session.
Firstly, there may be a case where the call set up message is sent to an access server AS which is currently in fact not serving the desired mobile subscriber MS, i.e. the mobile subscriber is not served by the corresponding access server, e.g. AS1, but served by another access server AS2 in the same telecommunication network. Since the call set up message was directed to the access server AS not serving the mobile station MS, no terminating call session can successfully be established. In FIG. 4c it may be noted that a direct call from AS1 to MS only takes place when the MS is really connected to the AS (with an IP address). Usually, the call connection passes through MSC1 (circuit switched).
Secondly, as is also indicated in FIG. 4c, when there are several access server AS1, AS2 in the same telecommunication network (which seems to be very likely due to the growing amount of internet calls), the packet switched call from the packet switched network (internet) will be converted into the circuit switched call in the corresponding xe2x80x9ccalledxe2x80x9d or xe2x80x9caddressedxe2x80x9d access server. Although it may be possible to set up the call if the access server happened to be selected which is currently serving the mobile station, another disadvantage may occur. Namely, the xe2x80x9ccalledxe2x80x9d or xe2x80x9caddressedxe2x80x9d access server may not necessarily be the access server which is located most closely to the mobile station when it roams in the mobile radio communication network. This means, that in fact there may be another access server located closer to the present location of the mobile station MS which is however not used since the connection is always built up through the xe2x80x9ccalledxe2x80x9d access server. The result is that the distance over which the call is handled as a circuit switched call is much longer than necessary. The above example describes the case that the mobile station is not served by an access server because there is as yet no circuit switched connection of a previously setup call connection. That is, in a case where there exists already one circuit switched connection between one access server AS and the mobile station and a further connection is to be setup, then the access server AS should be selected which is already used for the existing circuit-switched connection.
Thirdly, packet switched calls such as calls from the internet may use a plurality of functionalities (such as bearer services) which may not necessarily be supported by all access servers AS in the telecommunication network. In such case a xe2x80x9ccalledxe2x80x9d access server AS can not provide the functionalities necessary for the processing of the call from the packet switched network and thus the (call) connection set up will fail.
Fourthly, in particular when the second communication network is a mobile radio communication network, there is no flexible change of the used access server AS in particular when the mobile station roams during an ongoing call. That is, despite there might occur a situation in an ongoing call that another access server AS has a much closer distance to the new location of the mobile station, this access server is never used since only the xe2x80x9ccalledxe2x80x9d access server is capable of communicating with the mobile station MS.
As was explained with reference to the above FIGS. 4a, 4b, 4c there are several disadvantages when setting up (call) connections between a first and second telecommunication network in the prior art, in particular when the first communication network is a packet switched network and the second communication network is a circuit switched network. In particular, there is an inefficient use of the resources of the first and second communication network, since despite the provision of several access servers AS either the inappropriate access server is used or the complete call set up will fail since a wrong access node is called, i.e. an access node which can not provide the call processing funcitonalities needed for supporting the desired call.
Therefore, the object of the present invention is
to provide a method and a communication system where an efficient use of the resources of the first and second communication network is made when setting up a (call) connection between a first terminal of the first communication network and a second terminal of the second communication network.
This object is solved by a method for setting up connections from a first terminal of a first communication network to a second terminal of a second communication network, said connections being routed from said first terminal through one or more access servers to said second terminal, comprising the following steps:
a) sending a connection setup message from said first terminal to a first access server;
b) selecting a second access server from an access server identification means on the basis of a location of said second terminal in said second communication network and/or call processing specific characteristics indicating a specific type of call processing of the call in said first and/or second communication network; and
c) routing said connection setup message to said selected access server and setting up the connection from said first to said second terminal through said selected access server.
The object is also solved by a method for setting up connections from a first terminal of a first communication network to a second terminal of a second communication network, the connections being routed from the first terminal through one or more access servers to the second terminal, comprising the following steps:
a) sending a connection setup message from the first terminal to a first access server;
b) selecting a second access server from an access server identification means on the basis of a location of the second terminal in the second communication network and/or call processing specific characteristics (indicating a specific type of call processing of the call in the first and/or second communication; and
c) routing said connection setup message (to said selected second access server and setting up the connection from the first to the second terminal through said selected second access server; and
a method according to claim 1,
wherein the first communication network (TCP/IP) is a packet switched network (TCP/IP) and the second communication network (PLMN) is a circuit switched network (PLMN); and
a method according to claim 2,
wherein the circuit switched network is a mobile communication network, wherein said access server identification means is stored in the home location register; and
a method according to claim 3,
wherein said home location register stores a table indicating an access server address with respect to each mobile switching center, wherein said first access server provides information about the second terminal to said home location register which in turn determines the mobile switching center currently serving the second terminal on the basis of this information and reads out an appropriate access server address from the table stored in said home location register dependent on the determined serving mobile switching center.
The object is also solved by a method for setting up connections from a first terminal of a first communication network to a second terminal of a second communication network, the connections being routed from the first terminal through one or more access servers to the second terminal, comprising the following steps:
a) sending a connection setup message from the first terminal to a first access server;
b) selecting a second access server from an access server identification means on the basis of a location of the second terminal in the second communication network and/or call processing specific characteristics indicating a specific type of call processing of the call in the first and/or second communication network; and
c) routing said connection setup message to said selected second access server and setting up the connection from the first to the second terminal through said selected second access server; and
a method according to claim 1,
further comprising the following steps:
s1) sending a connection setup message containing an IP address or a mobile subscriber number from the first terminal to said first access server;
s2) extracting the mobile subscriber number on the basis of the connection setup message in the first access server and sending a send routing information message to a home location register of a mobile radio communication network;
s3) sending a provide roaming number message from said home location register to the currently serving the second terminal;
s4) reserving the mobile subscriber roaming number in said mobile switching center and returning the mobile station roaming number to said home location register in a provide roaming number result message;
s5) determining on the basis of the mobile station roaming number the access server address stored in the access server identification means and sending a send routing information result message to the first access server containing the mobile station roaming number and said selected access server address;
s6) sending data packets from said first access server to the second access server identified by said access server address; and
s7) sending an initial address message to the mobile switching center in order to build up a circuit switched connection between said mobile switching center and the second terminal.
The object is also solved by a method for setting up connections from a first terminal of a first communication networkto a second terminal of a second communication network, the connections being routed from the first terminal through one or more access servers to the second terminal, comprising the following steps:
a) sending a connection setup message from the first terminal to a first access server;
b) selecting a second access server from an access server identification means on the basis of a location of the second terminal in the second communication network and/or call processing specific characteristics indicating a specific type of call processing of the call in the first and/or second communication network; and
c) routing said connection setup message to said selected second access server and setting up the connection from the first to the second terminal through said selected second access server; and
a method according to claim 1,
further comprising the following steps:
s1) sending a connection setup message containing an IP address or a mobile subscriber number from the first terminal to said first access server;
s2) extracting the mobile subscriber number on the basis of the connection setup message in the first access server and sending a send routing information message to a home location register of a mobile radio communication network;
s3) sending a provide roaming number message from said home location register to the MSC/VLR currently serving the second terminal;
s4) reserving the mobile subscriber roaming number in said mobile switching centerand returning the mobile station roaming number to said home location register in a provide roaming number result message;
s5) returning the send routing information result message to the first access server and determining the second access server address on the basis of the call processing specific characteristics as indicated by the access server identification means;
s6) sending data packetsfrom said first access server to said determined second access server as identified by said access server address; and
s7) sending an initial address message to the mobile switching center in order to build up a circuit switched connection between the mobile switching center and the second terminal.
Furthermore, this object is solved by a communication system including at least one first communication network having a number of first terminals connected thereto and at least one second communication network having a number of second terminals connected thereto, connections between a respective first terminal and a respective second terminal being routed through one or more access servers, comprising:
a) an access server identification means storing a correspondence relationship between access server identifications and a location of second terminals in said second communication network and/or call processing specific characteristics indicating a specific type of call processing of the call in said first and/or second communication network;
b) selection means for selecting an access server from said access server identification means on the basis of a location of said second terminal in said second communication network and/or call processing specific characteristics;
c) routing means for routing a connection setup message sent from a first terminal to an access server selected by said selection means; and
d) setting up means for setting up the connection from said first to said second terminal through said selected access server.
Furthermore the object is solved by an apparatus for selecting an access server in a communication system including at least one first communication network having a number of first terminals connected thereto and at least one second communication network having a number of second terminals connected thereto, connections between a respective first terminal and a respective second terminal being routed at least through said selected access servers, comprising:
a) an access server identification means storing a correspondence relationship between access server identifications and a location of second terminals in said second communication network and/or call processing specific characteristics indicating a specific type of call processing of the connection in said first and/or second communication network;
b) selection means for selecting an access server from said access server identification means on the basis of a location of said second terminal in said second communication network and/or call processing specific characteristics.
Essentially, according to one aspect of the invention, information stored in an access server identification means is used in order to determine the most appropriate access server corresponding to the actual location of the second terminal (subscriber). An access server is selected from this access server identification means on the basis of the location of the second subscriber and/or specific call processing characteristics indicating a specific type of call processing needed by the call in the first and/or second communication network. When the most preferable access server has been selected, the packets from the transmitting subscriber station are then routed to this selected access server and a call communication takes place through this access server (and a respective MSC).
There are two possibilities how the packets can be rerouted to the selected access server AS. One example is where all packets are rerouted from the gateway access server GAS to the selected access server AS (preferably through a tunnel, e.g. by using the L2TP protocol (layer 2 tunneling protocol)). Another example is where the gateway access server GAS sends the IP address of the selected access server AS to the terminal TE in some kind of xe2x80x9cchangexe2x80x9d message, whereafter the terminal TE directly sends the packets to the selected AS (i.e. not through the intermediary of the gateway access server GAS).
Further advantageous embodiments and improvements of the invention are listed in the dependent claims. Hereinafter, embodiments of the invention will be described with reference to the attached drawings. In these drawings, the same or similar reference numerals designate the same or similar parts throughout.